Molding phenolic resin material for pulley, resinous pulley, and method of using molding resin material

ABSTRACT

A resin molding material for pulley essentially contains a novolac type phenolic resin, a glass fiber, an inorganic substrate other than the glass fiber, and an elastomer. The novolac type phenolic resin ranging from 25% by weight to 45% by weight, the glass fiber together with the inorganic substrate other than the glass fiber ranging from 45% by weight to 65% by weight, and the elastomer ranging from 0.5% by weight to 5% by weight, relative to the entire molding material are blended. As the inorganic substrate other than the glass fiber, for example, calcium carbonate is used. As the elastomer, for example, NBR is used. The phenolic resin molding material for pulley is molded to obtain a resin pulley.

TECHNICAL FIELD

The present invention relates to a phenolic resin molding material for apulley, a resin pulley, and a method for using the resin moldingmaterial.

BACKGROUND ART

Resin pulleys are commonly used as components of industrial machines orautomobiles because they are light in weight and capable of loweringnoises and lowering costs, compared to metallic pulleys. Among suchresin pulleys, a pulley made of phenolic resin is more frequently usedbecause it has advantages over a pulley made of thermosetting resin,typically of nylon that dimension accuracy is improved and deformationis less likely to occur.

A pulley made of phenolic resin is requested to have mechanicalstrength, dimension reliability, and thermal shock resistance. Also apulley made of phenolic resin is requested to have characteristicsappropriate for its fixing manner. When a pulley is fixed by using abolt, the pulley is requested to have excellent stress relaxation fromthe view point of preventing the bolt from loosing. On the other hand,when a pulley is fixed by introducing an insert inside the pulley, acrack may occur in the vicinity of the insert due to a difference inthermal expansion between the insert and the resin. For this reason, anexcellent thermal shock resistance is required. Thus in a pulley made ofphenolic resin, it is necessary to achieve a good balance among avariety of required properties at a high-dimensional level.

Conventionally, a fixing method by introducing an insert into a pulleymade of phenolic resin is often employed. In this case, an excellentthermal shock resistance is required as described above. For addressingthis, a glass fiber is blended into a phenolic resin in a phenolic resinmolding material for pulley in order to improve the thermal shockresistance, the mechanical strength and the dimension reliability.Patent document 1 describes mixing a phenolic resin, an elastomer, anorganic fiber, a glass fiber, and a powder silica, thereby obtaining aneffect of improving the heat shock resistance.

Patent document 1: Japanese Patent Application Laid-Open No. 2001-187958

DISCLOSURE OF THE INVENTION

The above prior arts insist that heat shock resistance can be improved,however, there is a room for improvement in stress relaxation.Accordingly, there arises an object to be solved for achieving a goodbalance of mechanical strength, dimension reliability, stress relaxationand thermal shock resistance at high level in a pulley made of phenolicresin, particularly, a phenolic resin pulley to be fixed by a bolt,which is used as a component for industrial machines or for automobiles.

The present invention was devised in consideration of the abovecircumstance, and it is an object of the present invention to provide aphenolic resin molding material for resin pulley having excellentmechanical strength, stress relaxation, thermal shock resistance, and toprovide a resin pulley molded therefrom.

The present invention provides a phenolic resin molding material forpulley, obtainable by blending ingredients including (A) novolac typephenolic resin, (B) glass fiber, (C) inorganic substrate (other thanglass fiber), and (D) elastomer, wherein proportions relative to theentire resin molding material of the ingredients are: (A) in the rangeof 25% by weight to 45% by weight, sum of (B) and (C) in the range of45% by weight to 65% by weight, and (D) in the range of 0.5% by weightto 5% by weight.

Since the resin molding material according to the present inventionincludes a novolac type phenolic resin, it sufficiently ensures thestress relaxation characteristic. Furthermore, since it includes theglass fiber, the mechanical strength can be ensured. Additionally, sinceit essentially contains the elastomer and the inorganic substrate otherthan the glass fiber, the thermal shock resistance is improved. Bycontaining combination of these materials in the proportions asdescribed above, it is possible to realize a resin molding materialachieving a good balance of the mechanical strength, the thermal shockresistance and the stress relaxation.

In the resin molding material according to the present invention, the(C) inorganic substrate may comprise at least calcium carbonate. Byusing calcium carbonate as the (C) inorganic substrate, it is possibleto further improve the thermal shock resistance by virtue of thesynergistic effect of the calcium carbonate and the elastomer.

In the resin molding material according to the present invention, the(C) inorganic substrate other than the glass fiber may substantiallyconsist of calcium carbonate. In the present description, the phrase“inorganic substrate substantially comprises calcium carbonate” means,for example, the fact that the ratio of calcium carbonate relative tothe entire inorganic substrate is not less than 90% by weight. Thisallows further improvement of the thermal shock resistance.

In the resin molding material according to the present invention, the(D) elastomer may comprise a diene rubber. In the present invention, thediene rubber may be acrylonitrile butadiene rubber.

In the resin molding material according to the present invention, the(D) elastomer may comprise polyvinyl acetal. In the present invention,the polyvinyl acetal may be polyvinyl butyral.

In the resin molding material according to the present invention, the(C) inorganic substrate may substantially consist of calcium carbonate,the (D) elastomer may substantially consist of acrylonitrile butadienerubber, and the proportions of these ingredients relative to the entireresin molding material may be: (A) in the range of 25% by weight to 33%by weight, (B) in the range of 25% by weight to 35% by weight, (C) inthe range of 25% by weight to 35% by weight, and (D) in the range of0.5% by weight to 2% by weight. This satisfactorily ensures improvementof the stress relaxation by addition of calcium carbonate. Therefore, itis desirably used as a resin molding material which is principallyintended for improvement of stress relaxation characteristic.

In the resin molding material according to the present invention, the(C) inorganic substrate may substantially consist of calcium carbonate,the (D) elastomer may substantially consist of acrylonitrile butadienerubber, and the proportions of these ingredients relative to the entireresin molding material may be: (A) in the range of 33% by weight to 42%by weight, (B) in the range of 45% by weight to 55% by weight, (C) inthe range of 2% by weight to 12% by weight, and (D) in the range of 1%by weight to 3% by weight. Accordingly, it is desirably used as a resinmolding material which is principally intended for improvement of heatcycle characteristics.

The present invention also provides a resin pulley molded from the resinmolding material. The resin pulley of the present invention is excellentin mechanical strength, thermal shock resistance and stress relaxation.

The present invention also provides a method for using a resin moldingmaterial in which the resin molding material is used in molding a resinpulley. The phenolic resin molding material for pulley according to thepresent invention is a molding material which is superior in mechanicalstrength, thermal shock resistance and stress relaxation to conventionalphenolic resin molding materials for pulley. This allows application toa variety of pulleys used as components for industrial machines andcomponents for automobiles.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, other objects, features and advantages as described abovewill be more apparent with reference to the description of followingpreferred embodiments and drawings associated thereto.

FIG. 1 is a front view showing a constitution of a pulley made ofphenolic resin according to the present embodiment.

FIG. 2 is a side view of the pulley made of the phenolic resin asillustrated in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

The phenolic resin molding material for pulley according to the presentinvention essentially comprises:

(A) novolac type phenolic resin,

(B) glass fiber,

(C) inorganic substrate (other than glass fiber), and

(D) elastomer.

The amounts of the ingredients (A) to (D), on the basis of the entirephenolic resin molding material for pulley may be as follows: (A): 25 to45% by weight,

sum of (B) and (C): 45 to 65% by weight, and

(D): 0.5 to 5% by weight.

In the following, explanation will be made on each ingredientconstituting the phenolic resin molding material for pulley according tothe present invention.

In the present invention, novolac type phenolic resin is used as the (A)phenolic resin. The novolac type phenolic resin is used because it hashigh cross-linking density, and is excellent in stress relaxation andlow in cost. The blending amount of the novolac type phenolic resin isin the range of 25% by weight to 45% by weight, preferably in the rangeof 27% by weight to 37% by weight, relative to the entire moldingmaterial. If the blending amount is too small, the elasticity increasesand the tensile elongation percentage decreases, to cause a decrease inthermal shock resistance, and the moldability deteriorates due to thereduced content of the resin. If the blending amount is too large, thestress relaxation decreases, the coefficient of thermal expansionincreases, the thermal shock resistance decreases, and the dimensionalchange due to molding shrinkage increases, with the result thatcharacteristics which are satisfactory for a resin pulley are difficultto be achieved.

In the phenolic resin molding material for pulley according to thepresent invention, a curing agent that cures the (A) novolac typephenolic resin may be contained. As the curing agent, curing agents thatare commonly used in novolac type phenolic resins can be used. Examplesof such curing agents include hexamethylenetetramine, resol typephenolic resins and the like. When hexamethylenetetramine is used as acuring agent, it may be used, for example, in an amount ranging from 14parts by weight to 20 parts by weight, relative to 100 parts by weightof the novolac type phenolic resin.

The phenolic resin molding material for pulley according to the presentinvention essentially comprises a fibrous inorganic filler. This fibrousinorganic filler contains no organic fibers. As such a fibrous inorganicfiller, for example, (B) glass fiber is used. The (B) glass fiber isblended so as to impart a mechanical strength to the molded product. Thecharacteristic of the (B) glass fiber is, for example, but notparticularly limited, from 10 μm to 15 μm in fiber diameter and from 1mm to 3 mm in fiber length. As a result of this, it is possible torealize a desirable operability in producing a molding material, as wellas a desirable mechanical strength of the molded product.

The adding amount of the (B) glass fiber may be, for example, 20% byweight or more, relative to the entire molding material. This ensuressufficient mechanical strength. Accordingly, it is possible to improvethe strength of the pulley on which high loads exert. Also, a pulleywith reduced thickness and reduced weight can be realized.

Examples of the (C) inorganic substrate used in the present inventioninclude, but are not particularly limited to, carcined clay, uncarcinedclay, wollastonite, talc, calcium carbonate, mica, and whisker ofpotassium titanate. Among these, for example, calcium carbonate orwollastonite, especially calcium carbonate is preferably used. As the(C) inorganic substrate, substantially only calcium carbonate may beused. Accordingly, it is possible to obtain a phenolic resin moldingmaterial for resin pulley having excellent mechanical strength, stressrelaxation, thermal shock resistance more stably. When calcium carbonateis used, the average particle size is, for example, in the range of 0.5μm to 20 μm, preferably in the range of 1 μm to 10 μm.

The adding amount of the (C) inorganic substrate may be, for example,not less than 1% by weight, preferably not less than 3% by weight,relative to the entire molding material. This securely improves thebalance of the mechanical strength, the stress relaxation, and thethermal shock resistance. The adding amount may be, for example not morethan 50% by weight, preferably not more than 40% by weight, relative tothe entire molding material 50% by weight. This ensures sufficientmechanical strength.

The blending amount of the sum of (B) glass fiber and the (C) inorganicsubstrate may be, for example, not less than 45% by weight, preferablynot less than 50% by weight, relative to the entire molding material.This ensures sufficient stress relaxation and prevents the bolt thatfixes the pulley from loosing. Also, it is possible to prevent thecoefficient of thermal expansion from increasing, and improve thethermal shock resistance.

The blending amount of the sum of (B) glass fiber and the (C) inorganicsubstrate may be, for example, not less than 65% by weight, preferablynot less than 62% by weight, relative to the entire molding material.This allows decrease in the elasticity and increase in tensileelongation percentage. Consequently, sufficient toughness is ensured,and the thermal shock resistance is improved. Also, the operability inkneading the molding material is improved.

The (D) elastomer used in the present invention is blended so as toimprove the thermal shock resistance. Although the kind of the elastomeris not particularly limited, the examples of the elastomer include dienerubbers such as acrylonitrile butadiene rubber (NBR), modified NBR,chloroprene rubber and styrene butadiene rubber; non-diene rubbers suchas ethylene propylene rubber; polyvinyl acetals such as polyvinylbutyral (hereinafter, referred to as “PVB”); carboxylic acid vinylesters such as vinyl acetate; and the like, and these may be used solelyor in combination. Among these, for example, nitrile rubbers such as NBRand carboxylic acid modified NBR are preferably used. These materialsare excellent in compatibility with a phenolic resin. Therefore, usingthese materials, it is possible to uniformly disperse the elastomer inthe phenolic resin. Accordingly, more excellent toughness is realized,and it is possible to further improve the thermal shock resistance ofthe resin molding material.

Also, by using a nitrile rubber such as NBR and carboxylic acid modifiedNBR or a PVB together with a novolac type phenolic resin, it is possibleto further improve the balance of the mechanical strength, the thermalshock resistance, and the stress relaxation.

The blending amount of the (D) elastomer is an important factor forrealizing a resin molding material having a good balance of themechanical strength, the thermal shock resistance and the stressrelaxation. The blending amount of (D) elastomer may be not less than0.5% by weight, preferably not less than 1% by weight relative to theentire molding material. This ensures sufficient tensile elongationpercentage. Hence, it is possible to ensure a sufficient toughness, andimprove the thermal shock resistance.

The blending amount of the (D) elastomer may be not more than 5% byweight, preferably not more than 3% by weight, relative to the entiremolding material. This prevents the stress relaxation and the mechanicalstrength from deteriorating and decreases the coefficient of thermalexpansion. Therefore, it is possible to improve the thermal shockresistance.

In the present invention, fillers other than the above may be blended asis necessary.

The composition of the phenolic resin molding material according to thepresent invention may be adjusted depending on the particular use. Forexample, as the resin molding material which is principally intended forimprovement of the stress relaxation characteristic, the followings canbe exemplified. Herein, a blending proportion of each ingredient isbased on the entire phenolic resin molding material.

Novolac type phenolic resin: in the range of 25% by weight to 33% byweight,

Hexamethyltetramine: in the range of 3% by weight to 7% by weight

Glass fiber: in the range of 25% by weight to 35% by weight

Calcium carbonate: in the range of 25% by weight to 35% by weight

NBR: in the range of 0.5% by weight to 2% by weight

As the resin molding material which is principally intended forimprovement of heat cycle characteristics, the followings can beexemplified. Herein, a blending proportion of each ingredient is basedon the entire phenolic resin molding material.

Novolac type phenolic resin: in the range of 33% by weight to 42% byweight,

Hexamethyltetramine: in the range of 3% by weight to 7% by weight

Glass fiber: in the range of 45% by weight to 55% by weight

Calcium carbonate: in the range of 2% by weight to 12% by weight

NBR: in the range of 1% by weight to 3% by weight

By employing such blending proportions, it is possible to furtherimprove the heat cycle characteristics by virtue of the synergisticeffect between the glass fiber and the acrylonitrile butadiene rubber.

The phenolic resin molding material of the present invention is producedby techniques known in the art. For example, in addition to the aboveingredients, a curing auxiliary agent, a mold release agent, a pigment,a coupling agent and the like are blended as necessary and mixed touniformity, and then melt-kneaded under heat by means of a singlekneader such as a roller, a co-kneader or a twin-screw extruder, or bycombination of a roller and other kneader, followed by granulation orgrinding, to obtain the objective material.

Next, explanation will be made on the pulley made of phenolic resin ofthe present invention. The resin pulley of the present invention isproduced by molding the aforementioned molding material.

FIGS. 1 and 2 show one example of a structure made of a phenolic resinof the present invention. FIG. 1 is a front view of a pulley made ofphenolic resin. FIG. 2 is a side view of the pulley made of phenolicresin illustrated in FIG. 1. In the pulley made of phenolic resin shownin FIGS. 1 and 2, an insert metal piece 2 is fitted into the pulley. Apulley 1 is formed with a fitting part into which the insert metal piece2 fits; an outer cylindrical part having a V-shaped groove; and a ribthat connects the fitting part and the outer cylindrical part.

The pulley made of phenolic resin of the present invention is usuallyobtained by compression molding, transfer molding, injection molding orinjection compression molding using a molding material of theaforementioned formulation while centrically placing a metallic insert.The molding may be conducted, in a molding condition of: moldtemperature of 170 to 190° C., molding pressure of 100 to 150 kg/cm²,and curing time of 1 to 5 minute(s), when compression molding isemployed. However, the condition is not particularly limited to this.

Since the pulley made of phenolic resin of the present invention isproduced by using the aforementioned phenolic resin molding material, itachieves a good balance of the mechanical strength, the thermal shockresistance and the stress relaxation.

EXAMPLES

The present invention will be explained by way of examples andcomparative examples. Mixtures of the formulations shown in Tables 1 and2 were kneaded with heating rollers of different rotation speeds, andformed into sheets and cooled. These sheets were grinded to obtaingranular phenolic resin molding materials.

The blended ingredient used in examples and comparative examples are asfollows.

(1) Resol type phenolic resin was produced according to the followingformulation.

A reaction vessel equipped with a reflux condenser stirrer, a heatingdevice and a vacuum dehydrator was charged with phenol (P) andformaldehyde (F) in a molar ratio (F/P) of 1:7, and then added with 0.5parts by weight of zinc acetate per 100 parts by weight of phenol. Thisreaction system was adjusted to pH 5.5, and allowed for refluxingreaction for 3 hours. Then the reaction was subjected to steamdistillation at 100° C. for 2 hours under a degree of vacuum of 100Torr, to remove unreacted phenol. Then, the reaction was allowed toreact for one hour at 115° C. under a degree of vacuum of 100 Torr, toobtain a solid of dimethylene ether type resol type phenolic resinhaving a number average molecular weight of 800.

(2) Novolac type phenolic resin: number average molecular weight of 700(A-1082, from Sumitomo Bakelite Company Limited)

(3) Hexamethyltetramine: Hexamine from Mitsubishi Gas Chemical CompanyInc.

(4) Glass fiber: Chopped strand with fiber length of 3 mm and fiberdiameter of 11 μm from Nippon Sheet Glass Co., Ltd.

(5) Calcium carbonate: SS 80 with average particle size of 2.6 μm fromNitto Funka Kogyo K.K.

(6) Clay: Insulite® from Mizusawa Industrial Chemicals, Ltd.

(7) Curing auxiliary agent: magnesium oxide

(8) Mold release agent: calcium stearate

(9) Coloring agent: carbon black

(10) PVB: S-LEC BX-5 from Sekisui Chemical Co., Ltd.

(11) NBR: PNC-38 from JSR Corporation TABLE 1 EXAMPLE EXAMPLE EXAMPLEEXAMPLE EXAMPLE EXAMPLE 1 2 3 4 5 6 FORMULATION wt. % NOVOLAC TYPEPHENOL RESIN 31 30 29 31 31 35 HEXAMETHYLENETETRAMINE 5 5 5 5 5 5 GLASSFIBER 30 27 31 50 30 50 CALCIUM CARBONATE 30 33 31 10 — 5 CLAY — — — —30 — NBR 1 2 — 1 1 2 PVB — — 1 — — — CURING AUXILIARY AGENT 1 1 1 1 1 1COLORING AGENT 1 1 1 1 1 1 MOLD RELEASE AGENT 1 1 1 1 1 1CHARACTERISTICS BENDING STRENGTH (MPa) 145 140 140 160 135 180COEFFICIENT OF 24 25 24 22 24 24 LINEAR EXPANSION (ppm) STRESSRELAXATION (%) 85.0 82.0 85.0 84.0 87.0 82.0 COLD HEAT SHOCK 150 175 150200 50 200

TABLE 2 COMPARA- COMPARA- COMPARA- COMPARA- TIVE TIVE TIVE TIVE EXAMPLEEXAMPLE EXAMPLE EXAMPLE 1 2 3 4 FORMULATION wt. % RESOL TYPE PHENOLRESIN 36 — — — NOVOLAC TYPE PHENOL RESIN — 31 26 47HEXAMETHYLENETETRAMINE — 5 4 8 GLASS FIBER 30 30 30 20 CALCIUM CARBONATE30 30 30 20 CLAY — — — — NBR 1 — 7 2 PVB — — — — CURING AUXILIARY AGENT1 1 1 1 COLORING AGENT 1 1 1 1 MOLD RELEASE AGENT 1 1 1 1CHARACTERISTICS BENDING STRENGTH (MPa) 140 150 110 130 COEFFICIENT OF 2824 35 45 LINEAR EXPANSION (ppm) STRESS RELAXATION (%) 68.0 86.0 70.065.0 COLD HEAT SHOCK 200< 25 100 100

A molding method of test specimens used for evaluating characteristicsand an evaluating method are as follows.

(i) Bending strength test was conducted according to JIS K6911.

(ii) Cold shock resistance: A metallic insert formed from a disc in 50mm diameter and 5 mm thickness attached with notches at two positionswas covered with a resin so that the thickness of the resin was 2 mmthick, thereby molding a test specimen. This test specimen was subjectedto a heat cycling test of 200 cycles, each consisting of 30-minutes heatexposures at temperature from −40 degree C. to 140 degree C.,alternately. Whether or not a cracking occurs was checked every 25cycles. The number of occurrences of cracking is represented in Table 1.

(iii) Stress relaxation: Stress relaxation test was conducted based onASTE F38B. A test was conducted at a test temperature of 100° C. and aclamping stress of 11.8 MPa, and a percentage of retaining fraction wasmeasured after 100 hours from the start of the test.

(iv) Coefficient of thermal expansion: Coefficient of linear thermalexpansion at 80° C. to 120° C. was measured by TMA.

Any of Examples 1 to 6 is a molding material in which a novolac typephenolic resin, glass fiber, an inorganic substrate and an elastomer areblended in predetermined amounts. The results shown in Tables 1 and 2demonstrate that molded products fabricated by molding these moldingmaterials achieved an excellent balance of the mechanical strength, thethermal shock resistance and the stress relaxation at elevated level,which is required for resin pulleys.

On the other hand, Comparative example 1 showed low stress relaxationdue to a resol type phenolic resin used therein, although the thermalshock resistance was very excellent. Comparative example 2 was inferiorin thermal shock resistance because it lacked an elastomer. Comparativeexample 3 was inferior in stress relaxation because of large blendingamount of the elastomer. The blending amount of the elastomer isimportant for obtaining a resin molding material which is excellent in abalance of the mechanical strength, the thermal shock resistance and thestress relaxation, and too large blending amounts are not favorable.Preferably, the blending amount of the elastomer is not more than 5% byweight, and a blending amount of not more than 2% by weight will enablesthe resin molding material to exert its performance more stably.Comparative example 4 was inferior in stress relaxation because of highblending amount of the resin ingredient.

1. A phenolic resin molding material for a pulley, obtainable byformulating ingredients, said ingredients comprising: (A) novolac typephenolic resin, (B) glass fiber, (C) inorganic substrate (other thanglass fiber), and (D) elastomer, wherein the proportions of eachingredients, relative to the entire resin molding material are: (A) inthe range of 25% by weight to 45% by weight, sum of (B) and (C) in therange of 45% by weight to 65% by weight, and (D) in the range of 0.5% byweight to 5% by weight.
 2. The resin molding material according to claim1, wherein the (C) inorganic substrate comprises at least calciumcarbonate.
 3. The resin molding material according to claim 1, whereinthe (C) inorganic substrate substantially consists of calcium carbonate.4. The resin molding material according to claim 1, wherein the (D)elastomer comprises diene rubber.
 5. The resin molding materialaccording to claim 1, wherein the (D) elastomer comprises polyvinylacetal.
 6. The resin molding material according to claim 1, wherein the(C) inorganic substrate substantially consists of calcium carbonate, the(D) elastomer substantially comprises acrylonitrile butadiene rubber,and the proportions of ingredients (A) to (D), relative to the entireresin molding material are: (A) in the range of 25% by weight to 33% byweight, (B) in the range of 25% by weight to 35% by weight, (C) in therange of 25% by weight to 35% by weight, and (D) in the range of 0.5% byweight to 2% by weight.
 7. The resin molding material according to claim1, wherein the (C) inorganic substrate substantially consists of calciumcarbonate, the (D) elastomer substantially consists of acrylonitrilebutadiene rubber, the proportions of ingredients (A) to (D), relative tothe entire resin molding material are: (A) in the range of 33% by weightto 42% by weight, (B) in the range of 45% by weight to 55% by weight,(C) in the range of 2% by weight to 12% by weight, and (D) in the rangeof 1% by weight to 3% by weight.
 8. A resin pulley produced by moldingthe resin molding material according to claim
 1. 9. A method for using aresin molding material comprising using the resin molding materialaccording to claim 1 for molding a resin pulley.